High Frequency Audiometry in C⁵-dip Cases

Abstract

Standard pure tone audiometry and high frequency audiometry were conducted on 404 workers who work at a paper mill where the noise level is over 80 phone (A). Out of 404 subjects, 87 (20%) were formed having C⁵-dip. Out of the 87 C⁵-dip cases, 24 indicated C⁵-dip in one side of the ears and 63 in both sides. No clear correlation was observed between C⁵-dip and age, but C⁵-dip tended to increase with the period of working. It appears that C⁵-dip is formed in the relatively early period after the start of work. There was a slight proportional relation between the noise level and C⁵-dip. Simular aging phenomenon as that in normal subjects was observed in the C⁵-dip cases in high frequency area. In the high frequency area of over 10kHz, no difference was observed between normal group and C⁵-dip group in the same age group.